Lasers have long been used for materials processing, including for marking, drilling, ablating, scribing, cutting, welding, and the like. While those lasers commonly used include CO2 lasers at 10.6 micron wavelength, 1.06 micron Nd:Yag lasers, near 1 micron Yb-doped fiber lasers, 532 nm green lasers, 355 nm UV lasers, and 266 nm UV lasers, the specific laser used for any application depends upon the detailed processing requirements. In some cases the average output power is the most important factor. For example for laser cutting and welding of metal, especially thick metal, the average output power has to high enough to melt the relatively amount of metal. In other cases the pulse energy is the most important factor. For example for drilling of materials, the pulse energy has to be high enough to remove the material in short period of time. In order to drill the material with clean edge, the pulse width of the laser is important as well. A shorter pulse can remove the materials in a shorter period of time, typically resulting in a hole with cleaner edge. For example a picosecond laser pulse can produce a cleaner hole than a microsecond laser pulse.
In many cases the laser wavelength is the most important factor, especially for processes wherein the absorption of laser energy is critical. When the materials exhibit stronger absorption, it is easier to perform the laser induced materials processing such as marking, cutting, drilling and welding.
Different materials however have different absorption and reflection spectrum while the typical wavelength bandwidth of a laser is only a few nanometers. In order to effectively expand the bandwidth, one solution is to combine different lasers. For example, U.S. Pat. No. 6,423,925 B1 by Sukhman, et al discloses an apparatus and method for combining multiple laser beams in laser materials processing systems, where each one of multiple laser sources are independently separately mounted on a laser material processing platform and their beam paths are combined by a combiner which includes one or more optical elements mounted in the laser material processing platform. The beam paths are parallel and collinear. The beam path of each laser source and the optical axis of the beam delivery system are each prealigned to the same predetermined reference and automatically coincide upon installation such that these components are rapidly and interchangeably interfaceable.
Similarly, US Patent Publication WO2005045476 A2 by Fu et al discloses a multi-headed laser apparatus combining two or more lasers in a single housing with a single output beam. U.S. Pat. No. 6,462,306 B1 by Kitai et al further discloses a system and method for materials processing using multiple laser beams. The system includes a laser supply system for supplying discrete machining beams that are separated from each other. The lasers can have different wavelengths. For example one is 1064 nm IR laser and the other is 355 nm UV laser.
However, the combining of multiple lasers for material processing applications have numerous drawbacks which are not addressed in the prior art. First, ensuring that two or more different beams are focused to the exactly the same location is extremely challenging. These laser wavelengths are produced by discrete lasers. The laser beams have to be aligned very well in order to reach the exactly the same location on the subjecting processing material after going through collimating and focusing optical elements. Any vibration and temperature induced misalignment could cause the two laser beams to focus on slightly different location, which will affect the material processing quality. For example, if the process is for drilling holes, the hole will not be very circular. If the processing is for cutting, the gap will be larger. If the processing is marking, the marked line will be wider.
But a further drawback is the fact that each laser typically has a linewidth of several a few nanometers, which can not cover the absorption band of many materials. The total laser bandwidth is still relatively small even several lasers are used. For example, the total laser bandwidth will still be mostly less than 10 nanometers when three lasers are combined. As a result such a system is typically custom designed for processing certain types of materials. Additionally, even when multiple lasers are combined, these laser wavelengths are still produced by discrete lasers, so the laser wavelengths are not continuously varied. And of course, the use of multiple lasers increases the price of the overall material processing system.